Raw laser beams may be produced from a variety of mechanisms. It is known in the art that raw laser beams need to be spatially shaped in order to have proper applications in areas such as laser illumination, laser processing (e.g., laser machining), nonlinear optics, etc. For example, a beam shaper can be used to spatially shape a raw laser beam to produce a flat-top beam. This flattened laser beam can then be used in lithography, holography, spectroscopy, and for a variety of material machining purposes.
Currently, laser beams are spatially shaped by a number of approaches, such as a beam scanning across the processing (or needed) area approach, an approach for redistribution of beam intensity with an array of micromirrors, a local adjustment of the intensity of the different parts of the beam with an optically addressable spatial light modulator approach, or an approach for exploiting the Fourier transform properties of lenses in the case of Gaussian beams.
Some of these approaches can be categorized as active methods that require the application of complicated and expensive equipment to control the beam intensity that often results in considerable losses in beam power. On the other hand, passive methods, such as exploiting the Fourier transform properties of lenses require the application of a Gaussian beam profile and can be used only to form a few special output beam profiles.
In particular, a simple approach for spatial beam shaping is based on a method of scanning a laser beam across a processing area. This is actually a quasi-laser shaping approach because it only controls an integral dosage of irradiation without a real spatial shaping across the beam. One example of a device exploiting such an approach is disclosed in U.S. Pat. No. 5,925,271, which is incorporated by reference herein in its entirety. Specifically, referring now to FIG. 1, the aforementioned patent discloses a spatial shaping device that includes stationary beam-shaping mirror 1 and rotary mirror 3. The device allows processing the surface of sample 7 with a homogenized dosage of laser beam exposure.
Laser beams can also be spatially shaped using a pre-programmable micromirror array to produce a spatial energy distribution suitable for marking, machining, and processing of materials. One example of a device exploiting such an approach is disclosed in U.S. Patent Application Publication No. 20020008091, which is incorporated by reference herein in its entirety. In this approach, the preprogrammed micromirror array redistributes the laser output beam energy to produce a desired two-dimensional machined pattern on a work piece. To create a special beam profile, this device uses a blocking diaphragm to adjust the intensity of every beamlet reflected from each single micromirror. One disadvantage of this approach is that this results in a large loss in the incident beam power. An additional disadvantage of this approach is the necessity to use complicated and expensive equipment to create the proper distribution of beam intensity.
WIPO Patent No. WO 01/04685 A1, which is incorporated by reference herein in its entirety, discloses an approach for producing a homogeneous intensity profile of a laser beam. In this approach, the laser beam impinges an optically addressable spatial light modulator whose local transmission or reflection properties depend in a non-linear manner on the local illumination intensity. Such a device in principle automatically generates an almost rectangular beam profile without any additional external influence. The basic disadvantage of this approach is that it results in a large loss in the incident beam power, a complicated device having a low damage threshold, and a necessity to exercise complicated control to create any special beam profile different from a homogeneous one.
U.S. Pat. No. 5,864,430, which is incorporated by reference herein in its entirety, proposes an approach that maps a Gaussian beam into a spatially shaped beam with a uniform irradiance profile by exploiting the Fourier transform properties of lenses. This approach does not require any controlling equipment and the approach has a rather high damage threshold. The basic disadvantage of this approach is that it operates only with an incident Gaussian beam and can be used only to form a few special profiles of the output beam.
It is therefore desirable to provide a system and method for spatial shaping of laser beams that overcomes the above-described shortcomings while retaining their advantages. In particular, it would be desirable to provide a system and method that can realize practically any spatial output beam shape without requiring complicated controlling equipment, without large losses in beam power, and/or without requiring a special distribution of the intensity of the initial (incident, raw, or input) laser beam.